Topographic maps were born as military tools for planning battles
Those wavy contour lines joining points of equal height began as military intelligence: armies needed to know the lie of the land for battles and defences, which is why Britain's national mapping agency is still called the Ordnance Survey. Technically, a map needs more than contours to count as topographic.
Strictly defined, a topographic map shows ground relief in large-scale, measured detail, and it also records the human landscape. Natural Resources Canada lists landforms, lakes and rivers, forest cover, administrative boundaries, towns and transport routes. Such maps differ from small-scale chorographic maps of whole regions, planimetric maps that leave out height, and thematic maps devoted to a single subject. In everyday speech, though, any map showing relief tends to get called topographic, which specialists regard as a misuse.
They are usually published as a series of sheets that fit together, sharing the same symbols and the same geodetic framework of projection, coordinates and datum, and official series use a national grid reference system. Unlike older cadastral surveys, which mostly recorded property and government boundaries, topographic surveys were about terrain and elevation.
France got there first: its Carte géométrique de la France, completed in 1789, was the earliest multi-sheet series to cover a whole nation. The Great Trigonometric Survey of India, launched by the East India Company in 1802 and continued by the British Raj after 1857, worked on a larger scale still and accurately measured Himalayan peaks from viewpoints more than a hundred miles away. Over time these maps became national assets for planning roads, railways and resource extraction. In the United States, mapping moved in 1879 to the newly created US Geological Survey.
In 1913 the International Map of the World set out to chart all of Earth's significant land at a scale of one to a million on about a thousand sheets. The project eventually failed, but its indexing system is still used. From the 1980s, printed sheets gave way to databases that users could turn into maps of any scale or content, such as the American TIGER system used for the 1990 census, and to digital elevation models built from aerial photographs, satellite images and radar. Because they were taxpayer-funded and unclassified, many of these datasets were free to use.
Source: Topographic map
